Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2008
Publication Date: February 19, 2009
Citation: French, A.N., Hunsaker, D.J., Thorp, K.R., Clarke, T.R. 2009. Evapotranspiration over a camelina crop at Maricopa, Arizona. Industrial Crops and Products. 29:289-300. Interpretive Summary: Economically productive crops that require low amounts of water and fertilization are needed for arid lands where water supplies are scarce. Camelina sativa, an oil seed crop, may fit these criteria as it has been shown elsewhere to be drought tolerant. Camelina is especially attractive because of its high Omega 3 fatty acid content. Camelina may potentially match yields from competitor crops such as Canola, but without higher levels of nitrogen. Although the crop has been cultivated for thousands of years, little is known about how and when to irrigate camelina. Between November 2006 and April 2007, an experimental plot of camelina was grown, monitored, and harvested to determine its water requirements. Crop water use was modeled using measurements of the crop temperature and weather data. The model agreed to within 1 mm/day in comparison to independent soil water measurements. Acceptable yields were obtained with much less irrigation water and nitrogen compared with other oilseed crops. This outcome supports the suitability of camelina as a new crop for regions such as central Arizona and will interest growers seeking guidance for irrigation.
Technical Abstract: Evapotranspiration (ET) over an oilseed crop, Camelina sativa, was evaluated for an experimental plot in Maricopa, Arizona between December 2006 and April 2007. Camelina (cv. Robinson) was grown in a 1.1 ha field in a randomized design containing 32 plots replicated for 4 levels of water depletion: 40%, 55%, 65%, and 75%. Six supplemental plots evaluated water stress with 85% soil water depletion. A surface energy balance model, utilizing meteorological and radiometeric observations within the plots, was implemented to estimate latent heat fluxes from the camelina canopy at 15 minute intervals during most of the growing season. The latent heat fluxes were then summed to produce daily estimates of ET. A distinct aspect of the model was the incorporation of canopy thermal infrared observations at 15 different locations, which allow plant water stress detection. The resulting ET values were compared with independent observations of soil water depletion, obtained from soil neutron probe profiles. Agreement on a plot-by-plot basis between modeled and observed ET values was very good, where RMSE were usually less than 0.8 mm d-1, R2 > 0.78, and bias<0.76 mm d-1. Average yield for the camelina crop was 1000 (plus or minus 310) kg ha-1. Average total oil content was 41.4 (plus or minus 3.8) % by weight. Oil content was predicted by yield with fair accuracy where R2 was 0.425 and RMSE was 2.36%. Correlation between resultant camelina yield and total ET was weak; the four main water depletion treatment plots showed no dependence of yield upon cumulative ET. The secondary water stress treatment plots, however, did show dependence, where a 20% reduction in cumulative ET resulted in a corresponding 24% reduction in yield. Hence seasonal camelina water minimally required 333-423 mm. The ET results showed that the surface energy balance is a feasible and valuable technique for monitoring crop water requirement over this potential oilseed crop. Further work is needed to characterize the relation between camelina yield and ET, including tests of different varieties and levels of fertilization.